Rene Descartes (1596-1650), French mathematician and philosopher. His most important scientific works were in mathematics. He created analytical or co-ordinate geometry, known as Cartesian geometry, in which geometrical problems are converted into algebraic forms. He attempted to explain planetary motions in terms of vortices surrounding the Sun. He is considered the father of modern philosophy, and stated, 'I think, therefore I am'. Artwork from 'Chaudieres et Machines a Vapeur' (1911) by French civil engineer Max de Nansouty (1854-1913), part of the 'Les merveilles de la science' series of 1867-1891 by Louis Figuier.